The World's conventional energy supplies, based mainly on readily available fossil sources, are rapidly diminishing. The main short-term alternative to the energy crisis, the harnessing of nuclear fission energy, inspires much controversy, and practical realization of nuclear fusion technology has not yet occurred.
Solar energy provides an obvious alternative energy source, which is clean and non-hazardous. Proper methods for the collection, concentration, storage, and conversion of solar light to be a practical solution is as yet lacking, since to date solar light is diffuse and intrinsically intermittent. Nonetheless, the feasibility of solar photovoltaic cells represents a desirable energy solution if as yet impractical.
One of the limitations of solar power to date is the large amount of silicon needed per kW for the preparation of solar cells, which problem is compounded by the fact that the preparation of doped high-grade silicon requires exceedingly large amounts of electrical energy.
One means utilized for the concentration of solar light involves the use of parabolic mirrors (or an assembly of such reflecting surfaces used for solar furnaces) or Fresnel lenses, for incorporation in gallium arsenide (GaAs) photovoltaics. The heliostat-type equipment needed for tracking of the daily apparent motion of the sun is expensive, and the method is inefficient due to losses of most of the diffused light, which constitutes about 60% of the light reaching the earth's surface in Europe and in most regions of the United States.
Planar luminescent concentrators were first proposed by Weber and Lambe (J. Appl. Optics 15, 2299 (1976)) and then elaborated in greater detail simultaneously by Goetzberger and Greubel (Appl. Phys. 14, 123 (1977)) and by Swartz, Cole and Zewail (Optics Letters/, 73 (1977)). The subject has been further analyzed by Batchelder, Zewail and Cole (Appl. Optics 18, 3090 (1979)) and by Goetzberger and Wittwer (Adv. Solid State Phys. 19, 427 (1979)) and Reisfeld et al. (Nature 274, 144 (1978); Nature 283, 281 (1980)) with emphasis on the use of fluorescent organic dye-stuffs. To date, all of the methods described using planar luminescent concentrators suffer the limitation of poor energy efficiency and great expense in construction of the devices. Moreover, in such devices, an escape cone for emitted light is an invariable outcome, as well as self absorption and low overall quantum efficiency of mixed dyes to absorb larger sections of the sun's radiation in an attempt to increase energy yields through Foerster energy transfer.
Use of multiple plate “tandem” configurations has not provided an ideal solution. Although such use results in efficient absorption, the concentration ratio is reduced by 3 to 4, depending on the number of plates employed and, as a result, entails using a large area of cells, thereby defeating the purpose of reducing the amount of cells required.
To date an ideal solar concentrator providing for high yields, with cost-effective processes for the preparation thereof is lacking.